I am a huge fan of "reward" and "loyalty" cards because if I am going to buy something, I might as well get something back.
For instance, I buy all of my gas at Super America because of its "Speedy Rewards" program. Every time you use your Speedy Rewards card, you earn points towards free merchandise or gift cards. You earn 20 points per $1 spent for food, drink, and merchandise and 10 points for every gallon of gas you purchase.
Unfortunately, if you want one of the "good" rewards like a $25 gift card, you'll need to be patient. It took approximately three years to earn my first $25 gift card, but now that my fiancé and I share a rewards card, we're on our way to earning a $25 gift card in less than 12 months!
Another reward card I use is from the salon I visit on a regular basis. You earn one stamp for every $40 you spend on products and services. After receiving 20 stamps, you can redeem your card for a $40 discount off any service or a $40 discount off any product purchase. I currently have 10 stamps so I am almost half-way there!
The third reward card I have is an AMC MovieWatcher card. You earn 2 points for each movie ticket purchased (with a maximum of 4 points per visit) and every time you accumulate 10 points, you get a free bag of popcorn or small soft drink or movie ticket (which you have the option of trading for a large soft drink and large popcorn). When you hit 100 points, you get a free night at the movies (i.e., free moive ticket, small popcorn, and small soft drink).
Even though I rarely go to movies at the theatre -- seriously, why pay $9.50 to see a movie when I can rent it on DVD for $3.99 (or for free) in just a few months? -- I use the card every time I go because I have absolutely nothing to lose by using it!
Finally, if you really want to maximize your spending power, use a credit card with a reward program to pay for all of your purchases, then it will be like getting twice the free stuff! Through the years, I've earned tons of gift cards to cool places like the Cheesecake Factory, Borders, and Crabtree & Evelyn because I use my credit card for everything -- gas, groceries, doctor bills, etc.
Just make sure you're able to pay your balance off in full each month, or else you're not really maximizing your spending power because the interest you'll have to pay is likely to be way more than the reward you're getting.